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 Briefing of centrifugal fan
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1、Briefing of centrifugal fan Usage and types： |
For general ventilation, centrifugal fans could be used in factory and the building. They could input and output air. The gas they conveyed should be air or unselfburn, no-harmful, no erosive gas. No cohered material is in the gas, the dust and grain contain should less than 150mg/m3, temperature lower than
80℃. We could product corrosion control fan adopting fiberglass. The blades could be made of aluminum
to convey easily burn and explored gas in anti-explored fans. The fan motor is also anti-explored to avoid the sparkle during running. The performance parameter is the same with general fans.
Centrifugal fans could be made into two types: LG and RD. Viewing from the one motor side, if the impellers rotate clockwise, it is called right hand ventilator .if the impellers rotate anti-clockwise, it is called left hand ventilator. The outlet place is shown by the outlet angle of the shell. |
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| 2、Performance and option： |
| The fan performance is displayed by flow volume, total pressure, main shaft speed, shaft power and efficiency, all of them are relative. See the follow formulas: |
| The performance is measured under standard condition. All the performance parameters in technology documents or ordering requirements are considered the standard ones.
So in the un-standard conditions, you should transform the parameters into the standard ones.
When atmosphere Pa=101325Pa, temperature t=20℃, the atom condition in the relative humidity φ=50％, air density η=1.2kg/m3, gravitation acceleration g=9.8m/s2 , the needed power could be counted according the formula：N=(Q?P)?K/(1000×η×3600×ηm)。 In the formula, Q-flow volume(m3/h), P-total pressure (Pa), η-efficiency (%),ηm- machinery efficiency (%), K- motor conservation accuracy parameter.
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disposal when the flow volume is larger or adequate
During using, the flow volume is often inadequate. It is mainly caused by the resistance fluctuation in the pipe net or working un-dynamic area. If the volume decreased gradually in a long time or abruptly in a short time, it is mainly caused by the plug of pipe net.
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Diagram of the direction of fan air outlet |
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If the inadequate flow volume happened in the first used of the fan, it mainly caused by the follow reasons:
1. The real resistance in the pipe net is much different from the counted one. From the general pipe net feature formula: P=KQ2, if the K is smaller than the counted K, the volume will be less.
2. Neglect the influence by the total pressure deviation △P. if the deviation is positive one, the volume will be larger; if the deviation is negative one ,the volume will be less.
The larger or smaller volume could be deal with the follow methods:
1）using flow saving equipment
2）changing the speed of fan
3）using higher or lower pressure fan
4）changing pipe net resistance parameter
note: the flow saving equipment is generally used. But when the real volume is much larger than the needed one, this method is uneconomic as its much more power asked.
If it is applicable, the methods two and three are generally used.
If the volume remains smaller when all the flow saving equipments were opened, we should adopt method four to supply the volume. Method two and three could also be used, except the direct driven motor and shaft connected fans. Only the fans with transmission device could change the speed by means of varying the wheel diameter. But the max speed of the fan could nor beyond the max one showed in the performance chart, and the power of it should recounted
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| 4、Installation and instruction |
Install instruments and tools should be well prepared.
Test the apparatus of fan, especially the impellers, main shaft and bearing.
The damage should be repaired.
Clear the bearing case with kerosene.
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The follow thing s should be pay attention to during installation：
1) on the connection section, machinery oil or lubricate grease should be smeared to avoid rusting and
Dismount troubles.
2)the position pin should be set before setting the screw of connection section.
3)No tools or materials left in the fan housing.
installation requirement:
1)The weight of air convey duct should not be set on the fan housing.
The interval between air inlets should be adjusted according to the blueprint, and they should be horizontal.
2) When install the air inlet duct, the duct could be directly connected with the flange. Holes could be punched in the flange to match the connection with pipe.
3) After installation, pluck the roller by hand or stick to make sure there is no impinge phenomenon and be flexible.
4)Protect cover should be set for the pulley after fan installation. If no duct was connected with the air inlet, you should also set protect net or other safety instruments (prepared by the users).
The motor power which fan adopts considers the machinery loss and the motor power conservation in certain condition, not refers to the required power when the air outlet is totally open.
The fan motor may be burn out when the fan just rotated when there is no duct was connected with the air inlet or outlet or with no around resistance. So to be safe, valve should be set on the duct of inlet or outlet, close the valve the start the motor, during the performance of motor, gradually open it until the using condition required. Pay attention to keep the motor current not to beyond the quantitative parameter.
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| 5. maintenance of centrifugal fans |
Fan maintenance workers should pay attention to the follow things:
1)fans could work just when all the instruments were ok.
2)make sure all the apparatus are right located after repaired.
3)clear the dust , dirty ,water in the fan and duct to avoid rusting.
4)repair the fan when it stopped.
Notices during the working of fan:
1)adjust the flow volume by means of flow saving equipment when the volume is too large or a required volume in a short time.
2)Check the fan when unmoral phenomenon happened during the start, stop and working of fan
3)3) Small troubles should be disposed in time during check. If the small troubles could not be deal with or big troubles are found out, the fan must be repaired.
4)4) Lube oil should be changed each repaired time and in certain times.
General troubles and reasons
General troubles：
1)bearing case vibrated violently
Reasons: friction between shell and air inlet or impeller
Inadequate steel rigidity or not firmed.
Loose of impeller rivets or distortion of wheel plate.
Loose of the connection between impeller axial plate and shaft
Loose of the screw between shell and pedestal, bearing mount and bracket, bearing cover and pedestal.
Bad installation of the outlet duct
Misbalance rotation.
Too narrow duct net and over-speed flow
2)bearing temperature is too high
Reason: the violent vibration of bearing case
Inferior lube oil and the dust ,grain, dirty it contains
Over loose or over tighten of the connect screw between bearing cover and pedestal.
Slant of the shaft and rolling bearing, the front and rear bearings are not concentric.
Damage of bearing
3)too large current and too high temperature
Reason: not absolutely close of inlet duct inside shutter or the flow saving valve
Too large flow volume or air leak
Over density air or over- pressure the fan conveyed
Too same voltage to the motor or single electricity corrupt
Influenced by the violent vibration of bearing
4)Slide out of belt
reason: the two pulleys are not in line which make the belt slides out from the small wheel.
5)tremble of belt
Reason: distance between the two pulleys is too close or the belt is too long |
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Dezhou Air Conditioner Equipment Co., Ltd.
Address： No.181,North Dongdi Road, Tianqu Industry Park ,Dezhou
TEL：0534—2356870 2358328
FAX：0534—2358326
huifeng888@263.net
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FAX：0318—7056261
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Ceil phone：13589940048
Contact ： An Shuwei |
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